This invention relates to multi-exposure controlled cameras wherein the diaphragm and/or shutter speed is selectively automatically controlled, and more particularly to exposure indicating devices for use in such cameras for indicating the particular exposure control condition to be carried out.
Multi-exposure cameras are operated such that the diaphragm is preferentially set by manual operation and the shutter speed is automatically controlled, or such that the shutter speed is preferentially set by manual operation and the diaphragm is automatically controlled. Also such cameras may be operated with the diaphragm and shutter speed maintained in a programmed relationship.
Problems are encountered in known multi-exposure cameras in the exposure control mode where the shutter speed is preferentially set and the diaphragm is automatically controlled. For example, if the shutter speed is preferentially set, there may result the following three different exposure conditions: (a) the diaphragm aperture can be determined with its possible range without changing shutter speed from its set value for providing an optimum exposure for the brightness of the object; (b) where, even if the diaphragm is stopped-down to its minimum aperture, there is over-exposure at the selected shutter speed because of excessively high brightness of the object; and (c) where, even if the diaphragm is brought to its fully open position, there is under-exposure at the selected shutter speed because of excessively low brightness of the object. It is undesirable to take photographs in either over-exposure or under-exposure conditions, represented by conditions (b) and (c) above, respectively.
With a multi-exposure controlled camera operated under the conditions (a), the diaphragm is controlled according to voltage signals commensurate with the preset shutter speed, brightness of the object and the film sensitivity, after which the shutter speed is controlled according to the intensity of light from the object which has passed through the prior controlled diaphragm. In this case, the controlled shutter speed substantially coincides with the preset shutter speed.
With the exposure conditions (b) and (c), an optimum diaphragm aperture cannot be obtained according to the voltage signals that are commensurate with a preset shutter speed. For the exposure conditions (b), the diaphragm is stopped down to a minimum diaphragm aperture, and then the shutter speed is controlled according to the intensity of light from an object passing through the minimum diaphragm aperture. In this case, the shutter speed to be eventually controlled will be faster than the preset shutter speed. However, for the exposure conditions (c), the diaphragm is held at its fully open position, and then the shutter speed is controlled according to the intensity of light from an object passing through the fully open diaphragm. As a result, the shutter speed to be eventually controlled will be slower than the preset shutter speed. As is clear from the foregoing, in the exposure control mode where the shutter speed is initially preset, the shutter speed for proper exposure may be equal to, faster, or slower than the preset shutter speed, as the case may be. Accordingly, because the eventual shutter speed control, in accordance with the particular exposure conditions, may deviate from the preset shutter speed, it is desirable to notify the camera operator, prior to photographing, of the exposure condition in which the picture is to be taken i.e., how the eventual shutter speed and diaphragm will be.
Additionally, in cameras of the type in which the diaphragm automatic control means is either made inoperable, or no diaphragm automatic control means are provided, and there is only means for manually pre-setting the diaphragm aperture, or in which the diaphragm is preferentially set manually and the shutter speed is automatically controlled, it would be advantageous for the camera operator to know, prior to exposure, whether the preselected shutter speed is equal to, faster, or slower than the eventual shutter speed to be controlled. Further, when the camera operator selects a shutter speed which falls within a range ensuring that the picture will not be blurred with the camera held by hands, it would be advantageous for him to know, prior to exposure, whether his photographing at such an eventual optimum shutter speed will cause a blurred photograph.